Where did all of the different people groups come from?

Source: Answers in Genesis

At the time of the dispersal at Babel, there were all types of skin tones, eye, mouth, nose, and ear shapes and sizes.  These genetic traits were specific to the families present.  After the dispersal, the families separated, carrying the same genetic traits and passing them on within their family.  In Asia, many of the people have the trait of black hair and an extra layer of fat in their eyelids.  Most likely, one family went to the Asian continent and spread out to form different countries (China, Japan, Korea, Vietnam, etc.) where all of these traits are still seen today.  Latin Americans and American Indians have similar skin tones, implying that they may all be direct descendants.  We see dark skinned people primarily living in hot regions, and light skinned people living in colder regions. 

As families trekked across the globe, the dark skinned people suffered in the colder areas because they did not get enough sun light, thus causing a vitamin D deficiency.  On the reversal, families that were light skinned suffered in hot areas because they got sun burns and skin cancers.  This is where survival of the fittest comes into play.  The fit ones—the dark in the sunny areas and the light in the not so sunny areas—were able to survive and continue reproducing, causing a great population density of their particular genetic traits.  To help better understand genetic isolation, see the following article: How can we understand genetics from dogs?